Optical Scanning Device and Image Forming Apparatus

The present invention relates to a scanning optical device and an image forming apparatus, for example, a scanning optical device used in an image forming apparatus using electrophotographic type such as a laser printer and a digital copy machine.

Conventionally, a scanning optical device provided with a semiconductor laser, a coupling lens, a condensed light lens, a deflector, a scanning optical system, a frame and a cover, as disclosed for example in Japanese Patent Application Laid-Open No. 2023-083740, is known. The semiconductor laser emits a laser light. The coupling lens converts the laser light from the semiconductor laser into a beam. The condensed light lens condenses the beam from the coupling lens in a sub scanning direction. The deflector includes a rotatable polygon mirror which deflects the beam from the condensed light lens in a main scanning direction. The scanning optical system forms the light from the deflector into an image on an image surface. To the frame, the deflector and the scanning optical system are fixed. The cover covers at least a part of the frame to which the deflector is disposed.

In this technology, the frame includes a first wall provided with a first opening for permitting passing of the beam toward the rotatable polygon mirror, and the condensed light lens blocks the first opening. With this configuration, the first opening for permitting passing of the beam from the coupling lens toward the rotatable polygon mirror is blocked by the condensed light lens. Therefore, entering of dust near the coupling lens from the opening is prevented and it is possible to suppress that dust moves toward the rotatable polygon mirror and adheres to the rotatable polygon mirror. In addition, it has a configuration that the frame includes a second wall provided with a second opening for permitting passing of the beam reflected by the rotatable polygon mirror, and a scanning lens closest to the rotatable polygon mirror of the scanning optical system blocks the second opening. With this configuration, it is possible to suppress that dust near the scanning optical system moves toward the rotatable polygon mirror and adheres to the rotatable polygon mirror.

However, since the deflector for rotationally driving the rotatable polygon mirror is provided with a driving board on which a driver IC is mounted, upon driving the deflector, the driver IC generates heat. In the conventional configuration, by blocking the opening around the deflector with the cover, the walls, the condensed light lens and the scanning lens, a space around the deflector is hermetically blocked, and there is concern that ambient temperature around the deflector may rise. In a case in which the temperature around the deflector rise, for example, the frame formed of resin may be thermally deformed, and positions of optical components such as various types of lenses and reflecting mirrors, which are encased in the frame, may fluctuate.

When the positions of the optical components fluctuate, irradiating position of the light beam irradiated on a photosensitive drum is changed, positions of the light beams on the plurally provided photosensitive drums are misaligned, and color misalignment occurs in a color image, in which toner images of four colors are superimposed, which may result in deteriorating image quality.

The present invention is conceived under such a background, and an object of the present invention is to suppress rise of ambient temperature around a deflector and to effectively realize dust proof around the deflector.

In order to solve the aforementioned problems, the present invention includes the following configurations.

Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

Embodiments of a scanning optical device according to the present invention will be described using the drawings. However, dimensions, material, shapes and relative dispositions of constituting components described in the Embodiments should be appropriately altered according to configurations of an apparatus to which the present invention is applied and various conditions, and are not intended to limit the scope of the present invention to the following Embodiments.

An Embodiment 1 of the scanning optical device according to the present invention will specifically be described with reference to Figures.

is a perspective outline view describing a scanning optical device. In the scanning optical devicein the Embodiment 1, each laser luminous flux L, L, Land Lemitted from a plurality of semiconductor lasers, which is a plurality of light sources, is scanned by a rotatable polygon mirrorprovided to a deflector. With the scanned laser luminous fluxes L, L, Land L, photosensitive drums of an unshown image forming apparatus are irradiated via optical members, respectively. The scanning optical deviceincludes the deflectorwhich includes the rotatable polygon mirror. The scanning optical deviceincludes a first imaging lens, second imaging lensesand, a BD lens, which are image forming members for the laser light and a first reflecting mirror, a second reflecting mirrorand a third reflecting mirror, which are reflection members (reflecting mirrors). Furthermore, the scanning optical deviceincludes an optical boxto which these are attached. The laser luminous fluxes L, L, Land Lemitted from the semiconductor laserbecome converged light by an anamorphic lens, in which a collimator lens and a cylindrical lens are integrally molded. Thereafter, the laser luminous fluxes L, L, Land Lare then limited in luminous flux width by a sub scanning aperture diaphragm and a main scanning aperture diaphragm, which are not shown, and form an image in a line shape having a certain width on a deflecting and reflecting surface of the rotatable polygon mirror. On laser control boardsand, a chip which controls the semiconductor laseris mounted. A beam detector (hereinafter, referred to as a BD)is mounted on the laser control board. The laser luminous flux Lis reflected, by the deflectorbeing rotationally driven about a rotational axis CZ, by the rotatable polygon mirror, deflected and scanned, and incident on the BDafter passing through the BD lens. At this time, based on a signal output from the BD(BD signal), writing out control of images of each color is executed.

In addition, in order to prevent unwanted light, which is different from the laser light for scanning the unshown photosensitive drum and is generated by the laser light being refracted and reflected by the lenses, etc., from reaching the photosensitive drum and causing image defects, a stray light prevention wallis provided. The stray light prevention wallis provided between the first imaging lensand the deflector, and a length and a height thereof are minimized to a size sufficient and necessary to suppress rise of ambient temperature due to the rotational drive of the deflector.

Incidentally, a direction parallel to the rotational axis CZ is defined as a Z direction, a direction in which the laser light is scanned by the rotatable polygon mirror, in other words, a longitudinal direction of the lens or the mirror is defined as an X direction, and a direction perpendicular to the X direction and the Z direction is defined as a Y direction. A dust proof wallwill be described later.

is a cross-sectional outline view describing an oblique incidence optical system of the scanning optical device. The oblique incidence optical system is an optical system in which the laser luminous fluxes Land Lare obliquely incident on a surface D of the rotatable polygon mirror. The incidence optical system, which is constituted by semiconductor lasersandand an anamorphic lens, are aligned vertically symmetrically with respect to an axis B, which is perpendicular to the rotational axis CZ. Of the plurality of light sources, the semiconductor laseris a first light source disposed with inclined at a desired angle θ with respect to the axis B. The laser luminous flux Lemitted from the semiconductor laseris incident on the surface D of the rotatable polygon mirrorobliquely from an upside with the angle θ.

On the other hand, the semiconductor laseris a second light source disposed with inclined at the desired angle θ with respect to the axis B. The laser luminous flux Lemitted from the semiconductor laseris incident on the surface D of the rotatable polygon mirrorobliquely from a downside with the angle θ. In this manner, by configuring the laser luminous fluxes Land Lfrom the two semiconductor lasersandabove and below to be incident obliquely from the upside and obliquely from the downside on the surface D, respectively, the laser luminous flux Land the laser luminous flux Lbecome separable into respective optical passages above and below after being reflected by the rotatable polygon mirror. In the Embodiment 1, the oblique incidence optical system is described using the laser luminous fluxes Land L, however, incidence optical system including light sources which emit the laser luminous fluxes Land Lillustrated inalso has the same configuration.

Next, using part (a) of, the scanning optical system after the laser luminous fluxes L, L, Land Lare reflected by the rotatable polygon mirrorin the Embodiment 1 will be described. Part (a) ofis a sub scanning cross-sectional view of the scanning optical system illustrating optical passages of the laser luminous fluxes L, L, Land L, which are deflected and scanned by the rotatable polygon mirror, until reaching photosensitive drums,,and

The scanning optical devicedeflects and scans each laser luminous flux L, L, Land Lemitted from the unshown plurality of the light sources, with the rotatable polygon mirror, with dividing the laser luminous fluxes into a scanning area Aand a scanning area A, which is on an opposite side to the scanning area Acentered on the rotational axis CZ of the rotatable polygon mirror. Since it is the oblique incidence optical system, in the Z direction, the laser luminous fluxes Land Lare reflected to the downside and the laser luminous fluxes Land Lare reflected to the upside by the rotatable polygon mirror. Thereafter, the laser luminous fluxes L, L, Land Lare incident on the first imaging lens. The laser luminous fluxes Land Lare reflected by the first reflecting mirror. Thereafter, after passing through the second imaging lens, the laser luminous fluxes Land Lare reflected again by the second reflecting mirror, pass through opening portions Hand Hprovided in a lidas a lid member, and reach the photosensitive drumsand, respectively.

In addition, after passing through the second imaging lens, the laser luminous fluxes Land Lare reflected by the third reflecting mirror, and after passing through opening portions Hand Hprovided in the lid, reach the photosensitive drumsand, respectively. The first imaging lensis a common lens for the laser luminous fluxes Land Land the laser luminous fluxes Land L, respectively, while the second imaging lensis disposed as a common lens for the laser luminous fluxes Land Land the second imaging lensis disposed as a common lens for the laser luminous fluxes Land L, respectively. Each imaging lens is fixed by an adhesive of UV light curing type, and each reflecting mirror is fixed by an urging member such as an unshown plate spring to the optical box. In addition, the lidis attached to the optical boxby an unshown screw.

The deflectorincluding the rotatable polygon mirroris disposed, in a horizontal direction, on a side closer to the photosensitive drumfrom a midpoint CH of the two of the photosensitive drumand the photosensitive drum. Here, the horizontal direction is a direction of a straight line Ywhich connects rotational centers of the photosensitive drumand the photosensitive drum, which are the two most distant of the four photosensitive drums. The deflectoris disposed on the side closer to the photosensitive drumfrom the midpoint CH of the two of the photosensitive drumand the photosensitive drum, and the laser luminous fluxes L, L, Land Lare incident on the photosensitive drums,,andfrom an oblique direction. By this, it becomes possible to widely open spaces T, T, Tand Ton a left side in the figure of each photosensitive drum,,and. As a result, it becomes possible for unshown toner cartridges to dispose of toner containers in the spaces T, T, Tand Tand to fill sufficient amount of toner to the toner containers.

Next, using part (b) of, air flows and air volumes (air flow rates) at opening portions of the scanning optical devicewill be described. Part (b) ofis a sub scanning cross-sectional view of the scanning optical device. The lidincludes the opening portions H, H, Hand Hfor permitting passing of the laser luminous fluxes L, L, Land L. Upon the deflectorbeing rotationally driven about the rotational axis CZ, the scanning optical devicedraws in outside air inside the scanning optical devicefrom the opening portions Hand Hdisposed relatively closer to the deflector, and air flows Kand Kare generated toward the rotatable polygon mirrorof the deflector. In the Y direction, the opening portion His disposed closer to the deflectorcompared to the opening portion H. Therefore, the opening portion His more susceptible to the rotation of the deflectorand the rotatable polygon mirrorcompared to the opening portion H, and the air flow Kflowing in through the opening portion His larger in the air volume than the air flow Kflowing in through the opening portion H. In addition, at the opening portions Hand H, by the rotational drive of the deflector, air is exhaled from the inside of the scanning optical deviceto the outside, and air flows Kand Kare generated. In a case in which the image forming apparatus is used in an environment with a lot of dust, etc. in an atmosphere, the dust, etc. enters the inside of the scanning optical devicethrough the opening portions Hand Hof the scanning optical device.

Next, results of study of the inventors (Study 1) will be described. In a simulation, the followings are found. That is, as to the air flow flowing into the inside of the scanning optical device, when comparing the opening portion closer to the deflectorand the opening portion further from the deflector, the entering air volume becomes larger at the opening portion closer to the deflector, while the entering air volume becomes smaller at the opening portion further from the deflector.

In Part (a) of, a simplified scanning optical device used in the simulation is illustrated. In a simplified scanning optical device, a deflectoris disposed approximately at a center of an approximately square optical box, and the optical boxis sealed by an unshown lid. In the simulation, in order to make air flows more visible, in a state in which the optical components such as lenses or reflecting mirrors are not present, three kinds of the lids are attached to the optical box and the air volumes (air flow rates) of the air flows at the opening portions with each lid are analyzed.

In part (b) ofthrough part (b) of, top views of simplified lids used in the simulation as viewed from above are illustrated. Part (b) ofshows a state in which an opening of the optical boxare covered by a lid, which includes opening portions H, H, Hand H. Incidentally, since the optical boxis covered by the lid, the deflectoris not actually visible and is illustrated by broken lines in the figure, and the same is also true in part (a) and part (b) of. In Part (b) of, in the Y direction, the deflectoris disposed approximately at a center between the opening portions Hand H. In addition, it is a configuration (Simulation 1) in which the openings Hand Hprovided to the lidare disposed, in the Y direction, with distances of Uand Uwith respect to a rotation axis CZof the deflector, respectively, and U=U.

Part (a) ofshows a state in which the opening of the optical boxis covered by a lid, which includes opening portions H, H, Hand H. Part (a) ofshows a configuration (Simulation 2) in which the openings Hand Hprovided to the lidare disposed, in the Y direction, with distances of Vand Vwith respect to the rotation axis CZof the deflector, respectively, and V<V. That is, the opening portion His closer to the deflectorthan the opening portion H.

Part (b) ofshows a state in which the opening of the optical boxis covered by a lid, which includes opening portions H, H, Hand H. Part (b) ofshows a configuration (Simulation 3) in which the openings Hand Hprovided to the lidare disposed, in the Y direction, with distances of Wand Wwith respect to the rotation axis CZof the deflector, respectively, and W>W. That is, the opening portion His closer to the deflectorthan the opening portion H.

Incidentally, in the Simulations 1 through 3, all openings are disposed so that intervals therebetween are the same. In the Y direction, including the two opening portions H, H, H, H, Hand H, which are disposed away from the deflector, the intervals between all of the opening portions are set to U+U=V+V=W+W.

shows results of the simulations.shows an air volume [m/min] at the opening portions of the lid, and a + side of a vertical axis represents an air flow direction flowing in from the outside to the inside of the scanning optical device. In, a graph on a left side shows the opening portions H, Hand Hfor permitting passing of the laser luminous flux L, and the distances from the rotational axis CZin the Y direction are U, Vand W, respectively. A graph on a right side shows the opening portions H, Hand Hfor permitting passing of the laser luminous flux L, and the distances from the rotational axis CZin the Y axis direction are U, Vand W, respectively.

In the Simulation 1 (part (b) of), since the opening portions Hand Hare disposed so as the distances of Uand Uwith respect to the rotational axis CZof the deflectorto be the same distance, i.e., U=U, the air volumes at the opening portion Hand at the opening portion Hbecome the same air volume.

In addition, in the Simulation 2 (part (a) of), since the opening portions Hand Hare disposed so as the distances of Vand Vwith respect to the rotational axis CZof the deflectorto be V<V, the air volume at the opening portion H, which is closer to the rotational axis CZ, is greater than that at the opening portion H.

In addition, in the Simulation 3 (part (b) of), since the opening portions Hand Hare disposed so as the distances Wand Wwith respect to the rotational axis CZof the deflectorto be W>W, the air volume at the opening portion H, which is further from the rotational axis CZ, is smaller than that at the opening portion H.

From the above-described results of the simulations, the following can be found. That is, it is found that of the two portions of the four opening portions provided to the scanning optical device, at the opening portion closer to the deflector, the air volume flowing into the scanning optical device becomes greater than that at the farther opening portion.

In part (a) of, a perspective view of the lid describing the dust proof wall is illustrated, and in part (b) of, a cross-sectional outline view of the scanning optical deviceas a dust proof walland the dust proof wallare viewed from the deflectorside in the −Y direction is illustrated. Air flows containing dust, etc. enter the inside of the scanning optical devicethrough the opening portions Hand Hof the lid. As shown in part (a) of, in the Embodiment 1, in order to effectively reduce an amount of dust reaching the rotatable polygon mirrorof the deflector, the lidincludes, in the Y direction, in a vicinity of the opening portion H, which is the closest in distance from the deflector, the dust proof wallas a wall portion. In more detail, the dust proof wallis provided at a position between the opening portion Hand the deflectorand closer to the opening portion Hin a direction perpendicular to the main scanning direction (X direction). The dust proof wallprovided to the lidis provided, parallel to the X direction, which is a longitudinal direction of the opening portion H, to stand (is standing) toward the optical box.

Here, the opening portion His farther from the deflectorin the Y direction than the opening portion H, and the air volume at the opening portion His smaller than that at the opening portion H. Therefore, to a vicinity of the opening portion H, a dust proof wall may not be provided, or a low standing wall, which is lower than the dust proof wallon the opening portion Hside, of a degree not to affect the air flow flowing in and out of the opening portion may be provided.

In addition, as shown in part (b) of, the dust proof wall(a second wall portion) of the lidis extended to a position in which the dust proof walldoes not have interference with the dust proof wall(a first wall portion) standing from the bottom surface (an installation surface of the deflector)of the optical box. The dust proof wallprovided to the optical boxincludes a dust proof walland a dust proof wall, which are provided parallel to the X direction and has different heights in the Z direction. Therefore, the dust proof wall is formed by the dust proof wallprovided to the lidand the dust proof wallprovided to the optical box, and an added length of the dust proof walland the dust proof wallin the X direction is approximately the same as a length of the opening portion H. Incidentally, the added length of the dust proof walland the dust proof wallmay be longer than the length of the opening portion H.

However, in the scanning optical device, in the area through which the unshown laser light passes, there is an area in which the dust proof wall is not present. For example, in a light passing portionfor the laser light being reflected by the rotatable polygon mirrorof the deflector, scanned and incident on the first imaging lens, and in a light passing portionfor the laser light being incident on the BD lens, the dust proof wall is not present in order not to block the laser light. Incidentally, the light passing portionis an opening provided to the dust proof wall

In this manner, the wall portion constituted by the dust proof walland the dust proof wallincludes the first light passing portion, which is a hole portion for permitting passing of the laser light deflected by deflector, and the second light passing portion, which is a hole portion for permitting passing of the laser light toward the beam detector BD of the laser light deflected by the deflector.

And, as the wall portion is viewed in an alignment direction of the plurality of the opening portions Hthrough H, for a space SPbetween the lidand the bottom surface(an area enclosed by a dashed line in part (b) of), approximately all area is covered by the wall portion, except the first light passing portionand the second light passing portion.

In the Embodiment 1, for the dust proof wall provided between the opening portion and the rotatable polygon mirror, the configuration of the two dust proof walls of the dust proof wall provided to the lid and the dust proof wall provided to the optical box is described, however, it may be a configuration in which the dust proof wall is provided only to the lid side, and in addition, it may be a configuration in which the dust proof wall is provided only to the optical box. In other words, in part (a) of, it is configured so that the dust proof walland the dust proof wallare combined to be equivalent to one dust proof wall, however, it is not limited thereto. The dust proof wallalone may be configured to be the dust proof wall which is the same as or longer than the length of the opening portion Hin the main scanning direction, or the dust proof wallalone may be configured to be the dust proof wall which is the same as or longer than the length of the opening portion Hin the main scanning direction. Furthermore, in part (b) of, the dust proof wallis constituted by the two dust proof wallsandhaving different heights, however, it may be constituted by three or more of the dust proof walls. Furthermore, the dust proof wallmay also be constituted by a plurality of dust proof walls having different heights. In addition, the dust proof wall provided to the lid and the dust proof wall provided to the optical box do not have to be disposed in the same position in the Y direction in part (a) of, but may be disposed in different positions in the Y direction from each other.

As described above, according to the Embodiment 1, the air flows entering from the opening portion Hside in part (a) ofmay reach the rotatable polygon mirror of the unshown deflector. However, since the air volume of the air flow is smaller on the opening portion Hside than that on the opening portion Hside, risk of the rotatable polygon mirror being contaminated by dust is lower on the opening portion Hside compared to that on the opening portion Hside. Therefore, by providing the dust proof wall in the vicinity of the opening portion closer to the deflector, which has the higher risk, it becomes possible to effectively prevent the entering of dust.

As shown in part (a) of, etc., the dust proof wallis provided only in the vicinity of the opening portion H, which is closest in distance to the deflector. In the Y direction, for the opening portion H, which is farther from the deflectorthan the opening portion H, the dust proof wall may not be provided thereto, or a low standing wall, which is lower than the dust proof wallon the opening portion Hside, of a degree not to affect the air flow flowing in and out of the opening portion, may be provided. However, in a case in which the standing wall is provided on the opening portion Hside, a height and a length of the standing wall is set in an arbitrary shape with taking into account balance between the air volume at the opening portion and temperature rise in ambient temperature around the deflector. In addition, on the opening portion Hside, the stray light prevention wallshown inis provided. In the scanning optical device, the unwanted light, which is different from the laser light for scanning the photosensitive drumand is generated by the laser light being refracted and reflected by the lenses, etc., may reach the photosensitive drumand cause image defect to occur. The stray light prevention wallis a configuration for preventing the unwanted light from reaching the photosensitive drum, and is provided so as a length and a height thereof to be minimum, unlike the dust proof wall provided on the opening portion Hside.

Next, results of study of the inventors (Study 2) will be described. In measurement results in which the ambient temperature around the deflector is measured by continuously driving the deflector of the scanning optical device, a configuration, in which the dust proof wall is disposed only in the vicinity of the opening portion closest to the deflector, and a configuration, in which the dust proof walls are disposed to both of the vicinities of the two opening portions disposed across the deflector, are compared. Then, it is found that the configuration in which the dust proof wall is disposed only in the vicinity of the opening portion closest to the deflector can reduce the ambient temperature around the deflector.

In, measurement results of the ambient temperature around the deflector when the deflector of the scanning optical device is continuously driven are shown. In, a vertical axis represents temperature rise [° C.] and a horizontal axis represents a driving time [min]. In, a thick solid line shows a temperature rise in a case in which a dust proof wall is provided only on the opening portion side closer to the deflector, a thin solid line shows a temperature rise in a case in which no dust proof wall is provided, and a broken line shows a temperature rise in a case in which dust proof walls similar to the dust proof wallare provided on both sides of the deflector.

When the deflector is continuously driven for 60 minutes, the temperature rise of the ambient temperature around the deflector becomes higher in the configuration in which the dust proof walls are provided on both sides of the two openings across the deflector than in the configuration in which the dust proof wall is disposed only in the vicinity of the opening portion closest to the deflector. In addition, the temperature rise in the configuration in which the dust proof wall is disposed only in the vicinity of the opening portion closest to the deflector is the same as that in the configuration in which no dust proof wall is provided.

Using this configuration, by providing the dust proof wall only on one side and configuring the length and the height of the stray light prevention wall provided on the other side at a minimum, it becomes possible to suppress the rise in the ambient temperature around the deflector and effectively prevent dust from entering inside the scanning optical device from the outside air. In addition, by this, it becomes possible to provide a scanning optical device which can achieve both suppression of the temperature rise of the scanning optical device and dust proof performance and prevent the degradation of image quality.

In the Embodiment described above, the opening portions are provided to the lid, and the dust proof wall for preventing the air flows flowing in through the opening portions of the lid from reaching the rotatable polygon mirror is exemplified, however, it is not limited thereto but the opening portion may be provided to the optical box. Part (a) ofis a sub scanning cross-sectional outline view describing a Modified Example of the Embodiment 1.

A scanning optical devicedeflects and scans each laser luminous flux L, L, Land Lemitted from an unshown plurality of light sources, by a rotatable polygon mirror, with dividing the laser luminous fluxes into a scanning area Aand a scanning area A, which is on an opposite side to the scanning area Acentered on a rotation axis CZof the rotatable polygon mirror.Since it is the oblique incidence optical system, in the Z direction, the laser luminous fluxes Land Lare reflected to a downside and the laser luminous fluxes Land Lare reflected upside by the rotatable polygon mirror.

Thereafter, the laser luminous fluxes L, L, Land Lare incident on a first imaging lens. The laser luminous fluxes Land Lare then reflected by a first reflecting mirror. Thereafter, after passing through a second imaging lens, the laser luminous fluxes Land Lare reflected again by a second reflecting mirror, pass through opening portions Hand Hprovided to an optical box, and reach photosensitive drumsand, respectively. In addition, after passing through a second imaging lens, the laser luminous fluxes Land Lare reflected by a third reflecting mirrorand after passing through opening portions Hand Hprovided to the optical box, reach photosensitive drumsand

The first imaging lensis a common lens for the laser luminous fluxes L, L, Land L, while the second imaging lensis disposed as a common lens for the laser luminous fluxes Land Land the second imaging lensis disposed as a common lens for the laser luminous fluxes Land L, respectively. Each imaging lens is fixed to the optical boxby an adhesive of UV light curing type, and each reflecting mirror is fixed to the optical boxby an urging member such as an unshown plate spring. In addition, a lidis attached to the optical boxby an unshown screw. A deflectorincluding the rotatable polygon mirroris disposed, in a horizontal direction, on a side closer to the photosensitive drumfrom a midpoint CHof the two of the photosensitive drumand the photosensitive drum. Here, the horizontal direction is a direction of a straight line Yconnecting rotational centers of the photosensitive drumand the photosensitive drum, which are the two most distant of the four photosensitive drums.

In the Modified Example, in order to effectively reduce an amount of dust reaching the rotatable polygon mirrorof the deflectorby air flow containing dust, etc. flowing inside the scanning optical devicefrom the openings portions Hand Hof the optical box, the optical boxhas the following configuration. That is, to the optical box, in the Y direction, in a vicinity of the opening portion H, which is the closest in distance from the deflector, a dust proof wallis provided.

The dust proof wallprovided to the optical boxis disposed parallel to a longitudinal direction of the opening portion Hand to stand from a bottom surfaceof the optical boxtoward the lid. For the opening portion H, since a distance from the deflectorto the opening portion His farther than to the opening portion H, an air volume at the opening portion His smaller than that at the opening portion H. Therefore, in a vicinity of the opening portion H, a dust proof wall may not be provided, or a low standing wall, which is lower than the dust proof wallon the opening portion Hside, of a degree not to affect the air flow flowing in and out of the opening portion Hmay be provided.